Wind Power is the conversion of wind energy into a useful form, such as electricity, using wind turbines.

The United States has just moved past Germany as the world's leading supplier of wind energy. Wind turbine companies are focusing on the U.S., a rapidly growing market, but there is a downside to this energy alterative.

Those swirling blades have been known to kill migratory bats. See, even fall, some species of migratory bats fly from Canada down south for the winter, but not all of them make it. A wind installation in Southern Alberta on the plains just east of the Rockies, an installation stands in their path. And each wind turbine there can take out several dozen bats a year during this migration season, and there are others like this all over North America.

But now the energy company that runs the Alberta wind farm has teamed up with a local university to see if there isn't a way to spare some of those bats from death on their way to their Mexican holiday. They came up with what could be a pretty good strategy for wind farms around the world, research that appears on the latest issue of the Journal of Wildlife Management.

Joining me now to talk about this is Robert Barclay. He is professor in the Department of Biological Sciences at the University of Calgary in Alberta. Welcome to SCIENCE FRIDAY.

Professor ROBERT BARCLAY (Department of Biological Sciences, University of Calgary): Thank you very much, Ira.

FLATOW: It seems like you had a pretty simple solution.

Prof. BARCLAY: Well, it seems simple after the fact, but, of course, these things are pretty complicated. And when we first started with this issue four or five years ago, it was a complete surprise that migratory bats would have an issue with wind turbines. As many listeners might know, the issue was one involving birds rather than bats.

FLATOW: And they thought about bats later. And simply, your solution is this: Just turn down or slow the blades down when it's down time, maybe nighttime.

Prof. BARCLAY: Well, yeah. Of course, the bats are migrating strictly at night. So it's an issue of them running afoul of the wind turbines at night. And they're pretty small animals, so they don't like to fly when it's really windy, which, of course, is when you're generating most of the electricity. And so TransAlta and the other companies we worked with said, well, we know that there's not a lot of bat activity when it's really windy. Most of it's when the wind speed is low. What if we tweaked the operation of the turbines so that they don't rotate as much when the wind is low? We're not generating a lot of electricity, anyway. Perhaps that will reduce fatalities.

FLATOW: All right. We're going to take a break and come back and talk more with Robert Barclay about reducing fatalities of bats in wind turbines. Our number: 800-989-8255. We're also twittering @scifri, @-S-C-I-F-R-I. You can send in your tweets. We'll be right back after this break, so please stay with us.

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FLATOW: I'm Ira Flatow, and this is SCIENCE FRIDAY from NPR News.

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FLATOW: I'm Ira Flatow. You're listening to SCIENCE FRIDAY from NPR News, talking with Robert Barclay, professor in the Department of Biological Sciences at the University of Calgary in Alberta, Canada.

He was talking about a novel, actually - gee, why didn't I - it sort of strikes me as gee-why-didn't-anybody-think-of-this-before solution to saving bats at night, when the wind is not blowing hard and when the bats are migrating, just turn down the rotation of the wind turbines.

Prof. BARCLAY: Well, and to be honest, when we started with this, we weren't sure whether the bats, like many birds, run into things, and they were running into wind turbines. And it wasn't necessarily that they were actually being hit by the blades. And as it turned out, many of them aren't actually hit by the blades, and yet they still die because they are near the turbines.

FLATOW: Well, wait. Let's stop there and explain that. How do they die if they don't smack into the blades?

Prof. BARCLAY: Well, it turns out that the blades of wind turbines, like the wings of airplanes and the wings of bats and birds, create low-pressure areas of air around them when air flows over them. So as the blades turn, particularly near the tips of the blades, there are these…

FLATOW: Vortex? A little vortex?

Prof. BARCLAY: There's a vortex, and that vortex has low air pressure in it.

FLATOW: Right.

Prof. BARCLAY: And when a bad goes through that, the lower pressure is very sudden, and that means that the lung air, the air in the lungs, expands rapidly and causes damage to the lungs.

FLATOW: Why doesn't that happen with birds?

Prof. BARCLAY: Birds have a very different respiratory system. Their lungs essentially are stronger and can withstand that sudden drop in air pressure. And so when we were looking for bats and birds underneath wind turbines, we'd frequently come across bats that looked perfectly intact, absolutely nothing wrong with them on the outside. When we looked inside, it turns out that their lung cavities were full of blood, and the little blood vessels in the lungs had been damaged. We never find birds that look like that.

FLATOW: Mm-hmm. You state in your research paper that when you did try your scheme of turning down the speed of the blades at the time the birds were migrating, at nighttime, that the wind farm revenues went down 3,000 and 4,000 Canadian dollars per month of the study. Do you think companies are willing to lose money like that?

Prof. BARCLAY: Well, it's obviously a cost-benefit analysis they have to go through, and that was three to $4,000 for 15 wind turbines. So it wasn't per turbine. So on a per-turbine basis, it starts to look economically not too bad.

Now, obviously, the economics of wind energy is different in different localities, and it's a competitive market. They have to compete with other types of electrical generation systems. But it's an industry that depends on a green image, a low environmental impact. And obviously, companies have to assess the costs of killing bats and birds versus the costs of perhaps reducing that through this technique.

FLATOW: Do you think other companies could make use of these operational changes that you've done?

Prof. BARCLAY: Absolutely. There are similar experiments going on in the U.S. as we speak with similar results, and it's not that a particular type of turbine or a particular location, necessarily, this is going to work better at than others.

As I said, bats are small animals. They simply can't fly very well when it's really windy. They fly mostly when the wind is low, and so if you start the turbine blades turning only when the wind reaches a higher velocity, then the bats can get through the wind farms without running afoul of the turning blades.

FLATOW: Let's go to the phones - John in Missouri. Hi, John. Welcome to SCIENCE FRIDAY.

JOHN (Caller): Hello, nice to be on the air. Yeah, I just had the comment that a lot of detractors of wind energy always use the whole bird-bat-dying scenario to kind of say that wind power is not a viable option when they don't ever also say or compare how many birds have - or bats or fish or all the other animals that have been killed by coal-fired power plants in the form of mercury poisoning or other types of contaminants. And I work in the renewable-energy industry, and every time this bird-bat thing comes up, it just makes me roll my eyes because I think it's such a small number that it's not that big a deal, as far as I'm concerned.

FLATOW: Professor Barclay?

Prof. BARCLAY: Well, of course, it's difficult to compare the environmental impacts of different types of electrical generation. But absolutely, coal-fired generators, we have lots of them out here in Western Canada. They have different environmental impacts, and you're sort of trying to compare apples and oranges.

FLATOW: Thanks for calling. 1-800-989-8255. Some tweets coming in from Twitter. This one reflects of different same-idea tweets from PoMo Media, who says: Bats use echolocation. So attach something that makes sound to the propellers. Bats will teach each other to avoid the sound.

Prof. BARCLAY: Yeah, and that was one of the first suggestions that came up, and the industry would love to have a whistle or something that people couldn't hear but bats could. Bats have very different hearing than we do. And the bat biologists around the table sort of thought about it and said, you know, we can't think of a sound we've ever produced that scared bats away. It always seems to attract them.

FLATOW: Really?

Prof. BARCLAY: There just don't seem to be that many sounds that bats might be afraid of. That being said, there is a group in the U.S. that's trying to produce very loud but ultrasonic - in others, above our hearing range - sounds that might interfere with bats' echolocation abilities - basically, make it harder for them to detect the sort of echoes that they're interested in. And if that's the case, they might avoid those sort of areas. So if you could put that sort of sound generation around wind turbines, it might mean that the bats go elsewhere during their migratory flights.